How Thermocouples Work on Ones Milwaukee Water Heater

Posted by on Dec 9, 2013 in Water Heater Repair Milwaukee

Ok, not to get too technical with you today, but Water Heater Repair Milwaukee wants to share some information on a water heater’s thermocouple.

The Family Handyman correctly concluded that “when thermocouples wear out, the pilot light goes out, the burner won’t light, and you don’t get any hot water.”

Standard design
Also called universal water heater thermocouple. It screws into below the gas valve and a probe on the other end slides into a holding bracket near the pilot light. It looks like a piece of copper wire.

Universal thermocouples come in lengths from 15 to 36 inches. An 18 or 24 inch will be enough for all residential water heaters utilizing universal kits. Almost all older waters heaters and many of the newer style units with a sealed burner compartment and a viewing window will use this thermocouple.
If you desire to make use of a specific replacement length simply eliminate your old one and determine it.

TCO design

Thermal Cut Off style has a re-settable thermal shut down switch integral into the thermocouple. In case of a flash fire or blow back from the burner the TOC will close down gas flow to the burner and pilot. In case of a closed down the TOC must reset itself after it cools down and permit you to relight the pilot. The TOC switch looks like a watch battery. You will only discover the TOC on newer design water heaters with seal burner compartments.

TOC non-resettable design

These thermocouples have a small TOC build inside television. They look comparable to a standard one except the diameter is larger about midways of television. When these TOC’s turn off they will not reset and have to be changed.

How Thermocouples Work

A pilot thermocouple sends out a tiny electrical current to the gas valve when the probe is warmed to a particular temperature. This electrical current tells the gas valve that the pilot is lit and its ok to send out gas to the burner if the thermostat asks for it.  There are some great images to illustrate how this works here.

To test a water heater thermocouple press the pilot button down on the water heater gas control valve. Then light the pilot. If after holding the pilot button down 30 to 60 seconds the pilot light doesn’t stay on when you release the button, the thermocouple is most likely the reason on older systems. The TOC or air flow might be the trouble on more recent units with a pilot light viewing window.

If the pilot does not light at all the issue is gas flow, gas control valve, TOC tripped.

Usual Thermocouple Problems

The most common issue is the pointer on the thermocouple probe deteriorates. It can quickly be replaced.

Thermocouple Repair

If the probe appears white in color this is carbon build up. It can keep the probe from getting hot enough to send out a signal to the gas valve. Try sanding it with emery cloth and relight the pilot. It must work for a while but keep a new thermocouple helpful.

  • The thermocouple probe should be in the pilot light flame.
  • The thermocouple needs to be screwed into the gas valve tightly.
  • Check the pilot thermocouple tube for kinks.

Water Heater Repair Milwaukee hopes this has actually been a great intro to a water heater’s thermocouple for you!